1. Field of the Invention
The present general inventive concept relates to a display apparatus and a control method thereof, and more particularly, to a display apparatus and a control method thereof, in which a moving picture and a still picture are displayed differently in a gradation level group.
2. Description of the Related Art
In a display apparatus that employs a time-sharing method for representing a gradation level, for example, in a plasma display panel (PDP), a digital mirror device (DMD), etc., there may be generated a false contour while the moving picture is displayed. Here, the false contour indicates a kind of afterimage due to a gradation level difference between a moving picture region and its adjacent region, wherein the gradation level difference is visually persisted and looks like a contour.
FIG. 1 is a schematic control block diagram of a conventional PDP in which the false contour of the moving picture is attenuated.
As shown therein, a conventional PDP comprises a reverse gamma correction part 101, a gradation level-limiting and error-diffusing part 102, a dither circuit 103, a motion detector 104, a selector 105, and a panel controller 106.
The reverse gamma correction part 101 changes an input video signal by the following equation (1). Here, the input video signal includes information about respective brightness levels of red, green and blue (RGB) data. Suppose that input and output brightness levels are represented as an integer, numerals to the right of a decimal point are an error of the brightness level.Y=X2.2   equation (1)(where, X is the input brightness level, and Y is the output brightness level)
The gradation level-limiting and error-diffusing part 102 reflects such error on the brightness of an adjacent pixel. That is, the brightness of the adjacent pixel is weighted with such error, and an error in the brightness of the adjacent pixel is reflected on the brightness information transmitted from the reverse gamma correction part 101.
A more significant function of the gradation level-limiting and error-diffusing part 102 is allowing the output of the reverse gamma correction part 101 to have the gradation level adapted to attenuate the false contour of the moving picture.
FIG. 2 is a table <Table 1> partially showing a gradation level representable by a weighted sub-field.
Referring to Table 1, the gradation level will be described in more detail.
One frame is divided into eight sub-fields sf1˜sf8, and the sub-fields sf1˜sf8 are weighted with the number of sustaining pulses 1, 2, 4, 8, . . . 128, respectively in sequence. Each gradation level is determined by a combination of luminance states of the sub-fields and is represented by a codeword, “1” as a luminance state and “0” as a non-luminance state. For example, the gradation level [3] is represented by a codeword of “11000000”. At this time, the gradation level corresponding to the selected codeword is proportional to the total number of the sustaining pulses per which light is emitted during one frame.
In Table 1, “using gradation level” is a gradation level used in attenuating the false contour of the moving picture; “dither gradation level” together with “using gradation level” is a gradation level used in displaying the still picture; and “dither value” is an inherent value of the dither gradation level, which is equal to a gradation level difference between the moving picture region and its adjacent region. Thus, the gradation level representable by the sub-fields as illustrated in <Table 1> ranges from [0]˜[255], but the gradation level corresponding to a predetermined codeword is selectively used.
In other words, the gradation level-limiting and error-diffusing part 102 limits the output of the reverse gamma correction part 101 to a predetermined gradation level group (“using gradation level”+“dither gradation level”) for displaying the still picture, and diffuses all errors toward the adjacent pixels.
When an input gradation level is the dither gradation level, the dither circuit 103 outputs a corresponding dither value to the selector 105. Further, the motion detector 104 detects the motion of an image based on the input video signal and outputs its detection result to the selector 105.
When the motion detector 104 determines that the input video signal is used for the still picture, the selector 105 directly transmits the input gradation level from the dither circuit 103 to the following panel controller 106. On the other hand, when the input video signal is used for the moving picture, the selector 105 changes the input gradation level received from the dither circuit 103 into the using gradation level for displaying the moving picture.
For, example, when the video signal has a brightness level of [44], the gradation level-limiting and error-diffusing part 102 changes the gradation level into the dither gradation level [47] and diffuses the error as much as [3] to the adjacent pixels. Further, when the motion detector 104 determines that the video signal is used for the moving picture, the selector 105 adds the dither value to and subtracts the dither value from the dither gradation level, thereby changing the dither gradation level into an adjacent using gradation level. In particular, in the case of an even frame, the using gradation level is changed by adding the dither value to the dither gradation level, that is, [47]+[16]=[63]. Oppositely, in the case of an odd frame, the using gradation level is changed by subtracting the dither value from the dither gradation level, that is, [47]−[16]=[32]. Consequently, the using gradation level has an average gradation level of [47] in terms of time, thereby displaying a picture near to an original picture.
FIG. 3 is a table <Table 2> showing a using gradation level for displaying a moving picture.
As illustrated in <Table 2>, even if not many using gradation levels are employed for displaying the moving picture, it is possible to attenuate the false contour because the gradation levels of the moving picture are not represented in detail. Oppositely, the using gradation levels employed for displaying the still picture are enough to represent the gradation level in detail.
However, in the conventional display apparatus, if the gradation level difference between the adjacent gradation levels among the using gradation levels is relatively large, the gradation level difference between the dither gradation level and the adjacent using gradation level becomes larger, and therefore a flicker is likely to be frequently made. The reason why the flicker is frequently made is that the larger the gradation level difference between the dither gradation level and the adjacent using gradation level is, the more frequently the selector 105 changes the gradation level group according to whether the video signal is used for displaying the moving picture. Further, the gradation level difference between the dither gradation level and the adjacent using gradation level is unnaturally represented like noise in the adjacent pixels according as the error-diffusing part diffuses a large error. Here, the foregoing dithering method allows upper and lower adjacent gradation levels to be repeatedly changed therebetween with respect to a time-series frame, thereby increasing the flicker.